This invention relates to a back material of a metal band saw which is welded with a blade material of high speed steel.
Hitherto, the metal band saws used are those which comprise a high speed steel blade material and an inexpensive low grade steel back material which are electron beam welded to save the expensive high speed steel. However, the conventional metal band saws which comprise a blade material and a back material such as AISI-1055, AISI 6150 etc., have the following problems: That is, when such metal band saws are quenched at a temperature of about 1200.degree. C and then tempered at a temperature of 540.degree. - 580.degree. C which are suitable heat treating conditions for the high speed steel of the blade material, since there are high quenching and tempering temperatures for the conventional back materials, toughness and hardness are lowered to cause reduction in tensile strength as back materials and furthermore cracks are formed in the back material part due to insufficient fatigue strength to cause breakage. Recently, materials difficult to be cut such as preharden steels and die steels which are high in hardness have been increasingly used as materials to be cut and high speed steels such as AISIM 40 series have been developed for cutting of materials which are more difficult to cut. Therefore, materials of higher tensile strength and toughness are required as back materials. Use of back materials of low tensile strength causes bend of cut surface. Moreover, metal band saws are used as endless band saws by driving with two wheels. Therefore, the back materials are subjected to repeated tensile stresses caused by bending and breakages occur in the back material part if fatigue strength of the back material is low. The metal band saws comprising a high speed steel blade material to which the conventional back material is welded have the problems as mentioned above. Thus, even in case the high speed steel of the blade material can still be used, the metal band saws may become unusable because of breakage in the back material part.